DISSERTATION RESEARCH: Inter-strain variation and evolution of resistance to phytochemicals in the bumblebee trypanosome parasite, Crithidia bombi

动物授粉维持着生态系统的生物多样性，每年为世界农业带来2150亿美元的价值。大黄蜂和其他野生传粉者使野生植物物种得以繁殖，每年为美国粮食生产贡献30亿美元；如果蜜蜂数量继续减少，大黄蜂的重要性可能会增加。然而，寄生虫导致美国大黄蜂数量减少了96%。植物产生一系列化学物质，称为“植物化学物质”，具有保护植物免受食草动物和病原体侵害的作用。这些化学物质可能是有效的抗菌剂；它们被用于传统和现代药物中，并赋予草药和香料以味觉和保存食物的特性。蜜蜂消耗的抗菌花蜜化学物质可以减少传粉媒介的感染，但也可能会选择对普通化学物质有抵抗力的蜜蜂寄生虫，从而失去药用价值。这个项目将加强对花卉景观如何影响和如何控制以减少传粉媒介疾病的理解。这项工作将使用大黄蜂寄生虫Crithidia bombi来确定植物化学物质如何影响寄生虫的生长和进化，特别是：(1)菌株在植物化学抗性方面是否不同？实验室数据表明，植物化学物质摄入的影响取决于蜜蜂感染的寄生虫菌株。这种变异可能反映或允许不同的菌株适合于响应共同的花化学型。本实验将测试8种花蜜植物化学物质对4株炸弹梭菌的影响。(2)菌株能否进化出对单个植物化学物质的抗性？长期暴露于植物化学物质中会产生耐受性基因型，从而降低传粉媒介的药用作用。实验将评估植物化学物质暴露4周后其抑制生长的作用是否会减弱。(3)植物化学混合物是否减缓了抗性的进化？在自然界，传粉者遇到的植物化学物质是混合的，而不是单一的化合物。在农业和临床研究中，当寄生虫同时暴露于多种化学物质时，耐药性的进化就会延迟，就像蜜蜂在不同的景观中觅食时一样。该项目将测试当寄生物暴露于植物化学混合物而不是单一化合物时，是否会延缓寄生物的植物化学抗性。结果将产生关于植物与动物病原体相互作用如何影响传粉者健康的假设；并提出使用植物化学物质缓解传粉媒介减少的策略。

Animal pollination maintains ecosystem biodiversity and is valued at $215B/year to world agriculture. Bumblebees and other wild pollinators enable reproduction of wild plant species and contribute $3B/year to US food production; bumblebees may increase in importance if honeybee populations continue to collapse. However, parasites have contributed to US bumblebee population decreases of up to 96%. Plants produce an arsenal of chemicals, termed 'phytochemicals', that confer protection against herbivores and pathogens. These chemicals can be potent antimicrobials; they are used in traditional and modern medicines and confer herbs and spices with gustatory and food-preserving properties. Antimicrobial nectar chemicals consumed by bees could reduce pollinator infection, but might also select for bee parasites that are resistant to common chemicals, which would then lose medicinal value. This project will enhance understanding of how floral landscapes affect and could be manipulated to reduce pollinator disease. This work will use a bumblebee parasite, Crithidia bombi, to determine how phytochemicals affect parasite growth and evolution, specifically: (1) Do strains vary in phytochemical resistance? Laboratory data suggest that effects of phytochemical ingestion depend on the parasite strain with which bees are infected. Such variation may reflect or allow differential strain fitness in response to common floral chemotypes. The proposed experiments will test the effects of 8 nectar phytochemicals on 4 C. bombi strains. (2) Can strains evolve resistance to individual phytochemicals? Chronic phytochemical exposure could select for tolerant genotypes, thereby reducing medicinal effects realized by pollinators. Experiments will evaluate whether growth-inhibiting effects of phytochemicals decrease over 4 weeks of phytochemical exposure. (3) Do phytochemical blends slow the evolution of resistance? In nature, pollinators encounter phytochemicals in blends rather than single compounds. In agricultural and clinical studies, evolution of resistance is delayed when parasites are simultaneously exposed to multiple chemicals, as would occur when bees forage in diverse landscapes. This project will test whether phytochemical resistance in C. bombi is retarded when the parasite is exposed to phytochemical blends rather than single compounds. Results will generate hypotheses about how plant interactions with animal pathogens influence pollinator health; and suggest strategies for using phytochemicals to mitigate pollinator decline.